研究目的
Investigating the fabrication of pure and near full-dense boron carbide ceramic using the laser-floating zone technique, and understanding the microstructure, composition, and mechanical properties of boron carbide grown at variable growth rates.
研究成果
The laser-floating zone method is a competitive and efficient technique to fabricate several boron-rich phases of boron carbide ceramics, including the superhard B6C phase under certain experimental conditions. The method allows control over the stoichiometry of the material, with the fabricated B6C showing hardness and elastic modulus close to theoretical limits. The technique offers a promising alternative for the fabrication of boron carbide ceramics with superior mechanical properties.
研究不足
The study is limited by the specific conditions of the laser-floating zone technique used, including the range of growth rates and the laser output power. The scalability of the technique to industrial levels and the detailed mechanism for carbon removal during the process are not fully explored.
1：Experimental Design and Method Selection:
The study utilized the laser-heated floating zone (LFZ) method with a CO2 laser to grow boron carbide rods from the melt. The rods were grown in argon atmosphere with a slight overpressure to avoid voids. Variable growth rates between 150 and 750 mm/h were used to evaluate their effect on the composition, stoichiometry, average grain size, and hardness of the resulting boron carbide ceramics.
2：Sample Selection and Data Sources:
Commercially available B4C powder (Grade HD20, H. C. Starck, Germany) was used as the starting material. Precursor rods were prepared by cold isostatic pressing and pre-sintering in a tubular furnace under ultra-high purity Ar.
3：List of Experimental Equipment and Materials:
CO2 laser for LFZ method, Philips X’Pert-Pro diffractometer for X-ray powder diffraction, field-emission scanning electron microscopy (FE-SEM) for microstructure study, EBSD system for orientation relationships, and nanoindentation tests for mechanical properties measurement.
4：Experimental Procedures and Operational Workflow:
The rods were grown with rotation of the pre-sintered ones at 50 rpm. X-ray powder diffraction patterns were recorded to analyze structural changes. Rietveld refinement was performed to determine crystallographic data and accurate compositions. Microstructure was studied using FE-SEM and EBSD. Nanoindentation tests were done to measure hardness and elastic modulus.
5：Data Analysis Methods:
Rietveld refinement using the FullProf program was performed for crystallographic data. Channel 5 software was used for EBSD data analysis. Nanoindentation data were analyzed to obtain hardness and elastic modulus values.
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